Data Detectives: The Ocean Environment Unit 4 – Marine Productivity Unit 4 Marine Productivity In this unit, you will • Discover patterns in global primary productivity. • Compare terrestrial and marine productivity. • Explore the key resources required for productivity. • Correlate variations in marine productivity with limiting resources. • Investigate sources of marine nutrients. • Synthesize observations to evaluate the causes of dead zones. NOAA The ocean provides up to 20 percent of the world’s food supply. 131 Data Detectives: The Ocean Environment Unit 4 – Marine Productivity 132 Data Detectives: The Ocean Environment Unit 4 – Marine Productivity Warm-up 4.1 Bounty from the sea Seafood makes up 20 percent of the world’s food supply, with over one billion people depending on its resources for survival. As seafood Sun harvests have increased over the past two centuries, populations of some species of marine life have decreased and have even become Light Water extinct. Given the ocean’s vast area, it is diffi cult to locate, monitor, and Dio Photosynthesis Carbon xide Respiration by track changes in stocks of commercially important fi sh and shellfi sh. by primary consumers, producers decomposers, and plants Th us, scientists frequently use satellites to indirectly assess the health of O Oxygen rg an c.) fi sheries and the ocean ecosystem. ic m es, et aterials (carbohydrat A key indicator of the ocean’s health is primary productivity, or the Waste heat Nutrients rate at which new organic material is produced through photosynthesis Figure 1. Photosynthesis and (Figure 1 at left ). Photosynthesis is the process by which plant cells respiration. containing the green pigment chlorophyll use sunlight to convert water and carbon dioxide into the food (sugars and starches) and oxygen needed by most other organisms. Satellites can measure the amount of Autotroph — (“self-feeder”) organism that makes its own food chlorophyll contained in single-celled plants in the ocean’s surface layer, rather than consuming other from which we can estimate primary productivity. organisms. Food chains (Figure 2) and more complex food webs (Figure 3) illustrate Heterotroph — (“other-feeder”) feeding relationships among organisms in biological communities. At the organism that consumes other organisms. base of food chains and webs are autotrophs, which produce their own food for growth and reproduction through photosynthesis. In the ocean, the primary autotrophs are phytoplankton, microscopic single-celled marine mammals sharks marine mammals jellyfish fish seabirds predatory fish zooplankton baleen whales zooplankton filter-feeding filter-feeding fish phytoplankton invertebrates Figure 2. Simple marine food chain. Arrows represent the transfer of energy from one organism to another through phytoplankton consumption. Figure 3. A marine food web. Bounty from the sea 133 Data Detectives: The Ocean Environment Unit 4 – Marine Productivity plants that drift near the ocean surface. Th e remaining organisms in food webs are heterotrophs, which obtain food by feeding on other organisms. Biotic community — group Th e preservation of each link in a food web is critical for maintaining of interdependent organisms diverse and healthy biotic communities. However, certain organisms are inhabiting the same region and more critical than others. interacting with one another. 1. Examine the complex marine food web in Figure 3 on the Anchovies — a type of small previous page. Add anchovies (A), tuna (T), and humans (H) fi sh, similar to sardines, that eat zooplankton. where you think they fi t best. Draw arrows as needed to show consumption of and by other organisms. Tuna — a type of large predatory fi sh that eat other fi sh. 2. What do you think would happen if all of the autotrophs were removed from the marine food web? 3. What do you think would happen if one of the heterotrophs, such as the predatory fi sh, were removed? 4. How do humans infl uence food webs? Respiration — process by which organisms oxidize or “burn” food, producing water and carbon dioxide. Photosynthesis requires four key ingredients: water, sunlight, nutrients, Nutrients — chemical and carbon dioxide. For marine autotrophs like phytoplankton, there compounds that are used by bacteria and plants as the building is plenty of water available in the oceans. Carbon dioxide is also blocks for organic material. abundant in ocean waters. It is released as a by-product of respiration, Common nutrients include: and it is readily absorbed into the ocean from the atmosphere. Th us, - water and carbon dioxide are not limiting resources for photosynthesis • phosphates (PO4 ) - or primary productivity in the ocean. However, marine productivity • nitrates (NO3 ) - is controlled or limited by the availability of the other two necessary • silica (SiO4 ) • iron (Fe3+) resources — sunlight and nutrients. 134 Bounty from the sea Data Detectives: The Ocean Environment Unit 4 – Marine Productivity 5. How do you think the availability of limiting resources might vary in the ocean? (Where or when would they be high or low?) 6. Considering the availability of limiting resources, where would you expect phytoplankton to be most productive or least productive? (Near the equator or near the poles? Near the coast or in the open ocean?) 7. How is the productivity of autotrophs important to society? Describe three diff erent ways in which a severe decrease in primary productivity would aff ect society. a. b. c. Bounty from the sea 135 Data Detectives: The Ocean Environment Unit 4 – Marine Productivity 136 Bounty from the sea Data Detectives: The Ocean Environment Unit 4 – Marine Productivity Investigation 4.2 The life-giving ocean Phytoplankton are tiny — several of them could fi t side-by-side across the width of a human hair — but collectively, they pack a wallop. Photosynthesis Phytoplankton are primary producers, serving as the fi rst link in almost every food chain in the ocean. Th ey transform water and carbon dioxide The general chemical equation for photosynthesis is: into carbohydrates, which they use for producing energy for growth and reproduction. Phytoplankton, in turn, are food for other organisms, sunlight passing carbohydrates and other nutrients up the food chain. Because 6 CO2 + 6 H2O C6H12O6 + 6 O2 carbon water glucose oxygen phytoplankton release oxygen during photosynthesis, they also play a dioxide (carbohydrate) signifi cant role in maintaining the proper balance of Earth’s atmospheric gases. Phytoplankton produce about half of the world’s oxygen and, in NASA doing so, remove large amounts of carbon dioxide from the atmosphere. Given the central role of phytoplankton in stabilizing the mixture of gases in Earth’s atmosphere and in providing food for other organisms, it is important to monitor their location and rate of productivity. Although it is impossible to directly measure the productivity of phytoplankton on a global scale, there are several ways of making indirect calculations. One method relies on the distinctive way that chlorophyll, the green pigment in phytoplankton and other plants, refl ects sunlight. By using satellites to measure the chlorophyll Figure 1. The MODIS (MODerate- concentration of the ocean surface layer, scientists can estimate the resolution Imaging Spectrometer) rate at which phytoplankton produce carbohydrates (Figure 1). Because instrument on the Terra satellite carbon is the key element in the process, productivity is measured in is the latest tool for measuring primary productivity from space. terms of kilograms of carbon converted per square meter of ocean surface (kgC/m2) per year. Global primary productivity In this exercise you will examine global primary productivity and its Primary productivity — the rate at which new organic material is relation to the factors that support phytoplankton growth. formed by photosynthesis. Launch ArcMap, and locate and open the ddoe_unit_4.mxd fi le. Refer to the tear-out Quick Reference Sheet located in the Introduction to this module for GIS defi nitions and instructions on how to perform tasks. In the Table of Contents, right-click the Primary Productivity data frame and choose Activate. Expand the Primary Productivity data frame. Th is data frame shows the average annual primary productivity for terrestrial and marine environments. During their respective winters, regions near the north and south poles receive little or no sunlight, making satellite measurements impossible. Nonetheless it is reasonable to assume that, with no sunlight during winter, there is relatively little primary productivity in these regions . The life-giving ocean 137 Data Detectives: The Ocean Environment Unit 4 – Marine Productivity 1. What colors represent areas of highest and lowest productivity? a. Highest. b. Lowest. 2. On Map 1, circle the land areas with the highest productivity using solid lines, and the land areas with the lowest productivity using dashed lines. Map 1 — Areas of highest and lowest productivity Turn off the Terrestrial Productivity layer. Using the Zoom In tool , examine, in detail, the areas with the highest marine productivity. When you are fi nished, click the Full Extent button to zoom back out to view the entire map. 3. Mark the ocean areas with highest productivity on Map 1 using the label H (high), and the ocean areas of lowest productivity using the label L (low). 4. Where is marine productivity generally a. highest? b. lowest? 138 The life-giving ocean Data Detectives: The Ocean Environment Unit 4 – Marine Productivity 5. Compare the locations of regions of high terrestrial and marine productivity on Map 1. Describe any geographic patterns or similarities in their distribution. Productivity and distance from coast Next, you will examine productivity near the coastline in greater detail. Turn off the Marine Productivity layer. Turn on and expand the Coastal Productivity layer. Click the Summarize button . In the Summarize window, select Coastal Productivity as the feature layer. Select Distance as the fi eld to summarize in the drop-down menu. Double-click Area (sq km) to display the statistics options, check Sum. Next, double-click Total Productivity (kgC) to display the statistics options, check Sum, and click OK.